Here is an image of NGC 6543 (the "Cat's Eye Nebula") taken with the Hubble
Space Telescope WFPC2 (J.P. Harrington & K.J. Borkowski)
in the three ions of oxygen: red is [O I] 6300Å, blue is
[O II] 3727Å,and green is [O III] 5007Å.

The study of planetary nebulae has been the focus of my
research. Particular interests have been construction of
photoionization models, radiative transfer problems, dust and thermal
infrared emission in planetaries, and observations of these nebulae with
a variety of instruments, including the Hubble Space Telescope and ISO.

Here is a list of my publications over the years:
Publications.
The Eskimo Nebula
In January 2000 the refurbished Hubble Space Telescope took new images
of the Eskimo planetary nebula. Here are computer
simulations which show what we think is the 3-dimensional structure
of the nebula and of how the wind from the central star has shaped it.
One in a long series of IAU Symposia on "Planetary Nebulae"
was held April 2006 in Hawaii:
(IAU Symp. No. 234).
Here is a poster I presented on the planetary nebula
NGC 2610.

The third conference in a series on asymmetric planetary nebulae was
held at Mt. Rainier, WA, during the summer of of 2003
(APN3).
I presented one of the summary talks; just a sampling of current
research: Emerging Directions and Critical
Research.

Here is an image of the protoplanetary He3-1475.
This HST image shows, in unprecedented detail, jets producing
a series of point-symmetric condensations. This color image was produced
by combining our (Borkowski & Harrington) image obtained through
the F658N [N II] filter of the HST WFPC2 (red) with a broad-band image
taken by Matt Bobrowsky (Orbital Sciences Corp.) through the F555W
filter (green).
Our paper (K.J. Borkowski,
J. Blondin and J.P. Harrington, Ap.J. Letters, 10 June 1997) discusses the
production of these features by oblique shocks.

We have a paper (Ap.J., 550, 778) on the kinematics of the jets:
Link to astro-ph

In addition to He 3-1475, three other nebulae have so far been imaged as
part of our Cycle 6 snapshot program to search for jets in planetary
nebulae. The target list has been drawn from nebulae with point
symmetric morphologies and from objects with spectroscopic indications
of high velocity flows. We presented images of them at the 190th AAS Meeting
[Borkowski, K.J., Blondin, J.M., & Harrington, J.P. (1997) BAAS, 29, 786 --
abstract 7.05]. North is up and east to the left in these images.

NGC 6210. This is an HST WF2 Image in [N II].
While the bright parts of this nebula are chaotic and very asymmetrically
placed with respect to the central star, there is also a fainter, symmetric,
two-lobed bubble. Along the axis of this bubble 17" to the northeast of the
star, is an elongated "bullet". This bullet is actually the brightest part
of one of the pair of point symmetric "arms" that can be seen in a deep CCD
image by Balick et al. (1992).

Hu 2-1 in H-alpha and in [N II]. The innermost ring seen in H-alpha,
with a major axis of 0.7", was observed with the HST PC by Bobrowski (1996).
The [N II] image, on the other hand, seems to show a cylindrical cavity which opens
into a bi-lobal structure.
In our deeper images, one can see how the axis of the nebular structure twists
counterclockwise as we progress outward.

Hb 4, also in H-alpha
and [N II].
We targeted this nebula because of the two outlying radial segments seen in the
CCD images of Schwarz, Corradi & Melnick (1992). The HST images show how complex
these features really are. The [N II] image of the northern segment, in particular,
shows a distinct "corkscrew" structure. The southern segment may have a similar
structure, but it is harder to trace. Also note that in the H-alpha image, the
southern segment is in line with the "nipple" in the faint arc of nebulosity
outside the bright core. A paper by Lopez, Steffen & Meaburn (1997) finds
that the corkscrew segments have velocities of +/- 150 km/sec. A new study has
just appeared in preprint "High velocity string of knots in the outburst of the
Planetary Nebula Hb4" by Derlopa, S. Akras, P. Boumis, and W. Steffen (arXiv:1901.05767).

In addition to thermal absorption and emission, the gas in stellar atmospheres scatters radiation. The main source of
scattering is free electrons (in hot stars) and Rayleigh scattering by atomic hydrogen (in cool stars). This scattering
leads to polarization of the emergent radiation. Based on available model atmospheres, we present the polarization and
limb darkening for stars of many types:

Over the years, I have made constant use of
`J', a terse computer language.
This page provides some examples of my J code
applied to astronomical problems,
particularly to radiative transfer problems involving polarization and line transfer.
( Kepler-16 and TRAPPIST-1 [Fig. 1,
Fig. 2, Fig. 3] too...)
NOTE: There is also a "J" app for android phones and iPhones/iPads. (see J page link above)

Here are a few souvenirs of Siebenburgen. In the 11th century, Germans
emigrated to Transylvania where they settled, built cities, and maintained
a separate identity in the land they called "Siebenburgen". These so-called
"Transylvanian Saxons" have now mostly emigrated back to Germany, unwilling
to lose their identity in communist Romania and its aftermath. But the
strange medieval character of the Transylvanian cities remains a witness
to their history. Here are a few images from my visit in August 1995.

One of the most charming of all the old towns is
Schassburg (Sighisoara in Romanian), which is crowned by the great
clock tower. A few steps beyond the tower is the house where Vlad Tepes
(AKA Dracula) was born. I found a restaurant on the second floor;
we had a very pleasant lunch there.
(Compare the tower with this 19th century print.)

The quintessential Saxon city was Hermannstadt
(Sibiu). The dormer windows in the roofs seem to regard you with sleepy
eyes, while the arched openings turn buildings into Bosch-like creatures.

Most characteristic are the "Kirchenburgen", the fortified churches, which were
a place of refuge in troubled times. This church is located near Kronstadt
(Brasov). The name is Tartlau.

In the wall surrounding the church at Mediasch (Medias), I found this
wonderful old door. More art deco than medieval,
it nevertheless carries an aura of mystery.

This is one of Claude's last etchings, completed about 1662 [Mannocci 43,
state v B (of vii)]. Apollo (in his role as the Sun god) leads
the Four Seasons as they dance to the music of Time. In the
background, men go about their business, for they cannot see the gods who
share the landscape with them.

"Now these things never happened, but always are." -- Sallustius

The inscription reads:

"Apollo in the act of obeying Time. Spring starts the
dance. Summer with its heat is not absent. Autumn follows with its sweet wine.
Winter marks its season."

Zinc plate etching, 5 1/8 x 8 1/4 in. This heavily-inked impression is titled "The Beech-tree"
at the lower left, although the title is usually given as "Beech Tree and the Valley
of the Little Beaver". Between July and September, 1919, Burchfield completed this and
at least ten other etchings. Only trial proofs of the plates were pulled by Frank Wilcox,
who had encouraged him to try this medium. In 1953 an edition of ten impressions was
printed from this plate, in connection with an exhibition of Burchfield's drawings.
This is Burchfield's only published etching. The fact that the impression shown here
is titled but not numbered suggests that this is a proof pulled in 1919. Many of the
proofs were titled. The Burchfield-Penney Art Center in Buffalo NY holds one of the 1953
impressions; it is not titled, but is numbered in the lower right corner.
In addition to this etching, there are a small number of other prints by Burchfield.
Here are most of them:
prints by Charles Burchfield.

Since it is hard to "erase" a mark on an etching plate,
Burchfield first did a series of drawings in violet indelible pencil as a sort
of discipline for the etching process. Here are two of these drawings:
"Under the Apple Tree" and
"Evening in the Alley". (Did you
notice the moon peeking through the trees in "Evening"?)

I gave a talk last year (8 Apr 2018) in Salem, Ohio to the Burchfield Homestead Society.
While it was not recorded live, I've reproduced my talk for the record here:Burchfield's Astronomy.